Only a tenth of England’s extensive floodplains are now fit for purpose – 90% no longer function properly – with the shortfall putting an increasing number of homes and businesses at risk of flooding, according to a new report.

Floods are more likely due to climate change and will claim higher economic costs unless action is taken to halt the damage to floodplains and restore some of their functions, warned the authors of the 12-month study – the first to paint a comprehensive view of England’s floodplains and their capabilities.

“We have ignored our floodplains,” said George Heritage of Salford University, co-author of the study the Changing Face of Floodplains, published by Co-Op Insurance on Thursday. “The changes to them mean water [from heavy rainfall] can flow much faster downstream, and can flow at the same speed as the water in the rivers.”

This accelerated flow has led to sudden and unstoppable deluges in recent years. For instance, Storm Desmond in 2015 affected more than 6,000 homes as rivers and streams burst their banks and spread water over floodplains. As these natural floodplains had been altered by man-made features, they no longer had the ability to store water, leading to rapid flows into urban areas which led to the devastation.

Storm Desmond caused more than £500m in damages, and misery for families excluded from their homes sometimes for months. The UK’s flooding bills are on the rise, with scientists warning of rocketing numbers of cloudbursts and periods of sudden and intense rainfall as climate change takes effect.

Floodplains act as natural “sponges”, soaking up excess water in their vegetation, forming natural buffers that hold back or divert rushing water after rain, and providing areas where rivers can breach their banks and wetlands can be replenished.

Intensive agriculture, increasing urbanisation, poor management of rivers and the draining of wetlands have left the vast majority of these natural features – many previously preserved for centuries by communities who understood their value – unable to fulfil these valuable functions, with some close to collapse.

Building on floodplains has been singled out for years as a key problem, but perhaps surprisingly was found to contribute only about a tenth of the damage in the study. Far greater is intensive farming, which has created artificially “smooth” and uniform landscapes, with hedgerows removed, large areas given over to single crops, wetlands drained and woods and grassland diminished. Farming accounts for nearly two-thirds of the loss of functioning floodplains, according to the study.

Natural floodplains cover about 5% of England, from upland areas and tablelands to low-lying marshes, such as the Somerset levels and the East Anglian fens. Once they were used for grazing for parts of the year, or left uncultivated. However, the exploitation of such areas accelerated in the middle of the last century, when wetlands were drained, hedgerows grubbed up and small farms gave way to bigger farming enterprises.

Today, the report found, 90% of England’s floodplains no longer function properly, with 65% modified by agriculture “meaning they’re now man-made, smoother surfaces”; 9% lost to urban and suburban building developments; 4% are now occupied by open water and 6% by semi-natural woodland and rough grassland; and only 0.5% is now natural or semi-natural wetland.

“It would be almost impossible to return the altered areas to their original state,” noted Heritage. “But it is possible to work with farmers to introduce features that would allow them to function better.”

These can include restoring hedgerows, which act as a brake on surface water, in place of wire fences or missing field barriers helps, as does keeping or replanting natural vegetation, and encouraging mixed use rather than uniform monoculture. These methods can also benefit farmers, by retaining topsoil that is easily washed away by flooding.

Another view of Cumbria, which has been hit by flooding repeatedly in recent years. Photograph: Dr Neil Entwistle/University of Salford

Good management is also essential: for instance, big trees growing near rivers can exacerbate flood damage, because they can fall into rivers. Traditional methods of pollarding trees result in smaller but stouter growth and more stable root structures, providing more robust river banks that can resist breaking.

“We would definitely see economic benefits,” from these changes, said Heritage.

Even small gains can be significant: Heritage said research had found floodplain restoration efforts could slow the speed of water flow by 10-15%, which may be enough to give vital breathing space for downstream communities as they cope with the impact of river flooding.

Martin Rogers, flood management adviser at the National Farmers’ Union, which assisted with the response to Storm Desmond, said: “Farmers are happy to play their role to reduce flood risk [in Cumbria]. However, natural flood management is not the only solution and we believe should only be used as part of a cohesive package of measures across the catchment. Where farmers provide a service in mitigating flood risk to help protect others, this must be part of a clear, planned strategy.”

Caroline Russell, the Green Party candidate challenging Labour leader Jeremy Corbyn in his Islington North constituency, said taxpayer payments to farmers should depend on providing such services.

“Farming subsidies should be used to make sure land is used to store water. We have completely messed up our floodplains, we are getting more water from climate change, and there is nowhere for the water to go. Land in the countryside has to work differently to protect the built-up areas from flooding,” she told the Greener UK Hustings conference on Tuesday in London.

Flooding, along with other environmental issues, has received little attention in most areas during the general election campaign.

The Environment Agency runs an online service allowing people to sign up to receive any flood warnings in their areas, and other basic advice includes putting aside emergency equipment such as torches and batteries, candles and matches, as well as non-perishable food and waterproof clothing.

Drawing up a “flood plan” is also advised, setting out actions including moving pets to safety, looking out for neighbours, taking treasured possessions upstairs, filling baths, sinks and containers with tapwater in case clean water supplies are shut down, and charging mobile phones immediately a warning is received.